Influence of synthesis route on the structure and electrochemical performance of biphasic (O'3/O3) NaNi0.815Co0.15Al0.035O2 cathode for sodium-ion batteries

Sodium-ion batteries have gained widespread attention for energy storage devices because of low cost and high abundance of sodium sources. In this paper, Biphasic O'3/O3 layered NaNi0.815Co0.15Al0.035O2 cathode materials (Na-NCA) are synthesized by using three different chemical routes viz. coprecipitation, hydrothermal and sol-gel methods. X-ray diffraction pattern and Raman analysis show the clear evidence of layered structure of all three samples. The kinetics of sodium ion [Na+] is deduced from cyclic voltammetry techniques and the values of Na+ ion diffusion coefficient is found to be 1.62×10−12, 1.11×10−13 and 1.71×10−12cm2s−1 for Na-NCA synthesized by coprecipitation, sol-gel and hydrothermal methods, respectively implying the better kinetics of Na+- ions in hydrothermal prepared Na-NCA cathode. Furthermore, the Cyclic voltammetry and differential capacity versus voltage (dQ/dV vs.V) studies reveal the good reversibility of phase transition in cathode prepared using hydrothermal route. Electrochemical testing indicates the better performance of hydrothermally prepared Na-NCA in terms of discharge capacity, capacity retention and energy density. This improved electrochemical performance is attributed to decease in solid electrolyte interface, reversible phase transition and high surface area as well as better diffusion coefficient. Additionally, evolution of phase after cycling process are also investigated and only single O'3 phase is observed for hydrothermal prepared Na-NCA cathode which is highly stable at room temperature.